Aluminum production apparatus



Sept- 23, 1969 P. H. scHEFFLER, JR 3,468,355

ALUMINUM PRODUCTION APPARATUS Filed Sept. 1l 1967 United States Patent OU.S. Cl. 164-266 9 Claims ABSTRACT OF THE DISCLOSURE Apparatus for thecontinuous production of light metals such as aluminum including anelectrolytic reduction cell for producing a liquid metal bath having asurface at an optimum distance below the cell electrode, an alloyholding furnace having upper and lower bath level limits, a conduit withpump for conveying metal to the alloy holding furnace and responsive tothe liquid metal bath level in the electrolytic cell, and a conduit witha pump for conveying liquid metal to a casting mold.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to apparatus for the continuous production of a light metal fromthe ore-reduction stage to the ingot casting stage. More particularly,it pertains to apparatus for the continuous production of aluminum.

Description of the prior art In the production of lightweight metalssuch as aluminum, the present practice is to periodically siphon moltenmetal from the individual electrolytic reduction cells and then cast themetal into so-called pigs. After solidifying and cooling the pigs arestacked on pallets for shipment to processing plants. Aluminum pigs areusually melted in a remelting furnace and alloying materials are added.The furnace is then tapped into transportable crucibles from whichingots are poured by the direct-chill process. The ingots are the rawmaterial for forging, rolling, extrusion, or drawing into the finalproduct form.

All of the foregoing stages are batch type processes involvingconsiderable manual labor and/ or manual control. Moreover, inasmuch asthe electrolytic reduction cells, the remelting furnaces, and the ingotpouring proccesses are frequently located at separate places, there is aconcomitant waste of time and heat.

From time to time attempts have been made to unite these separateprocesses into a continuous procedure in order to obtain the advantagesof minimal manual handling as well as a savings of time and fuel costs.

One of the more basic problems limiting the operation on a continuousprocedure basis is the removal of liquid metal from the electrolyticcells and conveying it to the holding furnaces where it is mixed withalloying materials. Similarly, there is a problem of conveying theliquid metal alloy from the holding furnace to the casting mold. Wherethe electrolytic cells, the holding furnace and the casting mold arepreferably disposed on the same elevation, the molten metal cannot beconveniently flowed by ygravity from one stage to the next.

Associated with the foregoing is the procedure of forming the metalremoved from the electrolytic cells into pellets of a convenient sizeand subsequently mixing them with pellets of other alloying elementssuch as copper, zinc, and magnesium in the holding furnace.

It has been found that the foregoing problems may be overcome inaccordance with this invention by providing interconnecting conduits andpumps for conveying liquid metal between the several stages in theproduction of a lightweight metal such as aluminum.

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Accordingly, it is a general object of this invention to provide analuminum production apparatus having minimal operating costs and powerconsumption.

It is another object of this invention to provide aluminum productionapparatus which is operative on a substantially continuous basis.

Finally, it is an object of this invention to satisfy the foregoingobjects and desiderata in a simple and expedient manner.

SUMMARY OF THE INVENTION Briefly, the apparatus of the present inventioncomprises electrolytic cell means for producing a liquid metal bath, analloy holding furnace having a bath level with upper and lower limits,and an alloy casting mold; first conduit means including a liquid metalpump for conveying metal from the metal bath in the electrolytic cell tothe alloy holding furnace, second conduit means including a liquid metalpump for conveying metal from the metal bath in the holding furnace tothe liquid metal casting mold, control means for maintaining an optimumlevel of crnetal bath in the electrolytic cell, the liquid metal pumpbeing responsive to the control means for increasing and decreasing therate of ow of metal in the first conduit means, and the liquid metalpump in the second conduit means `and being responsive to the upper andlower limits of the bath level in the casting mold for controlling therate of ow of metal into the casting mold.

IBRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of thenature and objects of this invention, reference is made to the drawings,in which:

FIGURE 1 is a diagrammatic View in accordance with the principles ofthis invention; and

FIG. 2 is a diagrammatic view of another embodiment in accordance withthe principles of this invention.

Similar numerals refer to similar parts throughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Aluminum is generally producedby an electrolytic reduction process in which alumina is dissolved inmolten cryolite from which molten aluminum is separated by electrolysiscontinuously from a molten solution of cryolite and alumina at about1000 C. The electrolytic reduction normally takes place in large cellsgenerally indicated at 1() in FIG. l which consists of a shell 12 linedwith carbon 14 forming an inner cavity 16 containing the cryoliteelectrolyte 18.

A carbon anode 20 extends into the electrolyte 18 to introduce currentwhich separates the metallic aluminum electrolytically and provides theheat to maintain a bath 22 of molten aluminum. During the electrolysis agap 24 between the lower end of the electrode and the surface of thebath 22 must be maintained at a critical dimension in order to maintainoptimum cell performance. Accordingly, as liquid metal 22 is withdrawnfrom the cell in a manner to be described below additional alumina mustbe added to the electrolyte 18 such as by an auger conveyor 26. Theconveyor 26 consists of a cylindrical casing 28, a helical tin 30 snuglydisposed within the casing, and a shaft 32 for rotating the fin withinthe casing. A variable speed motor 34 is provided for rotating theshaft. Alumina is introduced into the upper end of the casing 28 andenters the cell 10 as the tin 30 is rotated at the lower end of thecasing 28.

Molten aluminum is `withdrawn from the cell 10 by a liquid metal pump 36which is connected to the cell by a conduit 38 which extends from the-bottom of the cavity 16 to the lower end of the pump. The pump 36 has avariable speed and is composed of a ceramic rotor and housing to enableits handling of high temperature liquids and is more particularlydescribed in copending application Ser. No. 610,935, tiled Jan. 23,1967. The pump 36 is disposed within a shot tower chilling vessel 40through which a flow of inert gas coolant 42 such as argon or nitrogenwhich is introduced at the upper open end of the vessel through a duct44. The lower end of the vessel 40 is closed in a suitable manner suchas by bottom wall members 46. The pump 36 is of the centrifugal typewhereby liquid aluminum is dispersed radially from the upper end of thepump into the coolant 42 which causes the aluminum to solidify intosolid pellets that settle on the bottom Wall members 46 of the vessel40.

Although only one cell 10 is shown in the drawing, it is understood thata plurality of similar cells are usually provided and are connected bysuitable means such as similar conduits 38 to the lower end of the pump36. In addition, each conduit 38 may be provided with suitable closuremeans such as a freeze plug 48 to limit the flow of liquid aluminum froma particular cell for a given period of time to enable maintenance ofthe gap 24 between the anode 20 and the metal bath 22. Although theconduit 38 is suitably insulated to maintain a continuous liquid metalphase during operation of the pump 36, a portion of the conduit may -beuninsulated to permit the formation of the freeze plug 48 whennecessary. Suitable melting means such as a resistance heater may bemounted on and around the conduit to melt the plug 48 when withdrawal ofliquid metal 22 from the cell 10 is necessary.

The speed of the pump 36 is varied and matched with the speed ofoperation of the auger conveyor 26 by suitable means (not shown) tomaintain an optimum level of the molten bath and thereby derive theoptimum combination of conditions including the gap 24, amount ofalumina added to the cell, and the amount of aluminum withdrawn from thecell. The pellets (not shown) are removed from the chilling vessel 40 byan auger conveyor 50, the lower end of which extends into the lowerportion of the vessel 40 and the upper end of which empties into ahopper 52. The conveyor S is actuated by a motor 51 suiicient to keepthe vessel 40 empty and the conveyor includes a casing 54 which servesas a conduit for the pellets and the greater portion of which isoccupied by a rotatable helical fin 56.

As shown in FIG. 1, a holding furnace 58 is provided for the purpose ofmaintaining a metal bath 60' at about 1400 to 1500 F. The metal bath 60serves as a reservoir for a casting mold generally indicated at 62. Thefurnace -58 is preferably operated with a liquid metal circulatingsystem including a liquid metal pump 64, an outlet conduit 66, and areturn conduit 68. In conjunction with the circulating system aplurality of bins or hoppers 70y for the storage of pellets of othermetals, such as copper, zinc, and magnesium are provided withcorresponding conduits 72 which communicate with the return conduit 68for the addition of desired amounts of alloying elements. Each conduit72 is provided with a valve 74 to enable the ,addition of measuredamounts of the elements as required. Thus, the circulating systemmaintains a more homogeneous composition of the metal bath 60 andpermits the addition of equivalent or different amounts of alloyingelements and/ or aluminum from hopper 52 to the bath.

'Measured amounts of liquid metal 60 are withdrawn from the furnace S8through a conduit 76 leading to the casting mold 62. For that purpose avariable speed pump 78, similar to the pump 36, is mounted in theconduit 76. The casting mold 62 may consist of any one of a variety typeof molds. 'Ihe preferred mold shown in FIG. 1 is of a continuous castingtype including an upper cylindrical shell 80 and a bottom wall `82 whichis lowered as a liquid metal in the shell S0 solidiiies. For thatpurpose the bot- I 4 tom wall 82 is mounted on a shaft 84 and lowered ina conventional manner such as hydraulically.

The pump 78 is operated at a speed dependent upon the rate ofsolidication of the liquid metal 85 in the mold 62. The rate ofsolidication of the metal 8S controls the rate of movement of the shaft84. The level of the metal bath 60 in the furnace 58 varies during thecasting process in response to the rates of operation of the pump 78,the auger conveyor 50, and the shaft 84. But the necessity of adjustingthese rates to a nearly perfect synchronization is minimized as thecapacity of the furnace is increased.

The conduits 66 and 76 are provided with conventional insulating means-to prevent solidication of the liquid metal in the conduits. However,short segments of these conduits are uninsulated to permit the formationof freeze blocks 86 and 87, respectively, in a manner similar to thefreeze block 48 in the conduit 38. The freeze blocks 86 and 87 areeliminated by `the application of heat such as by the mounting of aresistance heater around the segment of the conduits Where the freezeblocks are formed.

Another embodiment of the invention is shown in FIG. 2 which differsfrom that of FIG. 1 in that it is an entirely liquid metal operationwithout Ithe formulation of aluminum pellets. Accordingly, all parts inFIG. 2 are similar to those of FIG. 1 except as described hereinbelow.

In FIG. 2, the conduit 38 extends from the cell 10 to an insulatedliquid metal reservoir 86. A liquid metal pump 88 similar to the pumps36 and 78 is provided in the conduit 38. The liquid metal reservoir 86is suiliciently large to hold an adequate amount of liquid metal 89which is conveyed by a pump 90 in an insulated conduit 91 to the furnace58.

Alloying elements such as copper, zinc, or magnesium are added to theliquid metal 60 circulating through the conduit 68 in measured amountsthrough the valves 74. However, auger conveyors may be substituted forthe valves 74.

It is understood that the above specification and drawings are merelyexemplary and not in limitation of the Invention.

What is claimed is:

1. Apparatus for continuously processing molten metal comprising a metalreduction means for producing a liquid metal bath,

an alloy holding furnace having a bath level with upper and lowerlimits,

an alloy casting mold,

first conduit means for conveying metal from the metal bath 'm thereduction means to the alloy holding furnace,

second conduit means for conveying molten metal from the holding furnaceto the liquid metal casting mold, control means for maintaining anoptimum level of metal bath in the metal reduction means,

meter means in the rst conduit means for controlling the rate of flow ofmetal conveyed from the liquid metal bath to the alloy holding furnace,

means connected to the meter means and responsive to the control meansand for increasing and decreasing the rate of flow of metal in the rstconduit means in response to a respective increase and decrease in thelevel of the bath, and

second meter means in the second conduits means for controlilng the rateof ow of metal conveyed from the alloy holding furnace to the castingmold and being responsive to the rate of solidifcation of metal in thecasting mold.

2. The apparatus of claim 1 in which the metal reduction means is anelectrolytic cell.

3. The apparatus of claim 1 in which the first conduit means comprises aliquid metal pump.

4. The apparatus ol" claim l in which the second couduit means comprisesa liquid metal pump.

S. The apparatus of claim 1 in which the control means for maintainingrthe metal bath level in the reduction means comprises means for addingmeasured amounts of metal ore to the reduction means.

6. The apparatus of claim 1 in which the liquid metal pump in the firstconduit is responsive to the level of the liquid metal bath in thereduction means.

7. The apparatus of claim 1 in which the liquid metal pump in the secondconduit is responsive to the level of the liquid metal in the castingmold.

8. The apparatus of claim 2 in which the first and second conduit meanseach comprise a liquid metal pump, and

the control means for maintaining the metal bath level in theelectrolyte cell comprises a means for adding measured amounts of metalore to the cell.

9. The apparatus of claim 8 in which the means for adding measuredamounts of metal ore to the cell and the meter means in the rst conduitcomprise auger conveyors.

References Cited UNITED STATES PATENTS J. SPENCER OVERHOLSER, PrimaryExaminer V. RISING, Assistant Examiner U.S. C1. X.R. 164-155

